package PTA_work;

import java.util.Scanner;

/* 请在这里填写答案 */
class NotSanjiaoException extends Exception {
    public NotSanjiaoException() {
        super("三边长不能构成三角形");
    }
}
class Sanj {
    double x,y,z;
    double area;
    public Sanj(double x, double y, double z) throws NotSanjiaoException {
        this.x = x;
        this.y = y;
        this.z = z;
        if(!(x+y>z && y+z>x && x+z>y)) {
            throw new NotSanjiaoException();
        }
    }

    public double getArea() {
        double s = (x+y+z)/2;
        return Math.sqrt(s*(s-x)*(s-y)*(s-z));
    }
}
public class test_6_73{
    public static void main(String args[])   {
        try {
            Scanner scan=new Scanner(System.in);
            double a,b,c;
            a=scan.nextDouble();b=scan.nextDouble();c=scan.nextDouble();
            Sanj sj=new Sanj(a,b,c);
            System.out.println("三角形面积为："+sj.getArea());
        }catch(Exception e) {
            System.out.println(e);
        }
    }
}